Packaging structure and method of an image sensor module

ABSTRACT

This invention relates to a packaging structure and method of an image sensor module. The method comprises: providing a transparent substrate having a first patterned conductive layer; carrying an image sensor integrated circuit chip having a photosensitive active area and at least one passive chip on the transparent substrate, wherein the photosensitive active area faces the transparent substrate; forming an insulating build-up film over the transparent substrate; and forming a plurality of conductive vias in the insulating build-up film wherein the ends of the conductive vias are connected with the passive chip or the first patterned conductive layer of the transparent substrate while the other ends of the conductive vias are exposed on the surface of the insulating build-up film. The packaging method is capable of down-sizing the construction of the image sensor module and simplifying the processing steps.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flip chip packaging structure andmethod of a semiconductor integrated circuit and, in particular, to aflip chip packaging structure and method of an image sensor.

2. Description of the Related Art

Multilayer packaging is one of the most advanced processes forfabricating semiconductor integrated circuit (IC) products. With themultilayer package, the space between the electrodes of an IC chiphaving multilayer package electric circuits is increased; the chip isprotected from the internal stresses of the package and any externalstresses, and an appropriate thermal path for dissipating heat generatedby the chip and an electrical interconnection are established. Themethod for packaging an IC chip is deemed as the system used for thepackage, dominating the total cost, performance and reliability of thewhole package chip.

IC chip packaging generally falls into two categories, that is, hermeticpackages and non-hermetic packages. When a chip is packaged by thehermetic package, it is isolated from the external environment by avacuum seal or a particular kind of gas surrounding the chip. Ingeneral, such hermetic packages are the ceramic packaging used for highefficient applications. In other words, when a chip is packaged by thenon-hermetic packages, it is not substantially isolated from theexternal environment. In this light, the hermetic packages have higherfabrication cost than the non-hermetic packages. Even so, the hermeticpackages are still needed in some particular applications such as imagesensors or pressure detectors. The recently advanced application withthe plastic packaging has expanded the scope of usage and theperformance of the hermetic packages. Since the traditional method forfabricating products is good for automatic batch processing, the plasticpackages are highly cost-effective.

An IC chip packaging recently developed is ball grid array (BGA)packages, which can be used for both the ceramic packaging and theplastic packages. The BGA packages use a plurality of solder balls orbumps to serve as interconnections between the IC chip and other microelectronic devices providing electricity, mechanical support or heattransfer. The solder balls or bumps cause the IC chip to be fixedlymounted on a circuit board, and are electrically connected with theconductive pattern of the circuit board. The BGA techniques are includedin the bonding technology defined as the controlled collapse chipconnection (C4) or the flip chip technology.

The flip chip technique can be used to bond various circuit boardscomprising a ceramic substrate, a printed circuit board, a flexiblecircuit and a silicon substrate. The solder bumps are generally disposedon a conductive bond pad of an area array of a flip chip, the conductivebond pad being electrically interconnected to an electric circuit traceon the flip chip. Since micro-electric circuits of the flip chip willgenerally perform various functions, a number of solder bumps willtherefore be required. As a rule, each side of the flip chip has a sizeof about 13 mm, resulting in solder bumps jammed on the perimeter of theflip chip. Thus, the conductive pattern of the flip chip is consisted ofvarious conductors spaced apart appropriately equal to or less than 0.1mm as a matter of course.

Leadless chip carrier (LCC) packages are generally found in an imagesensor such as a charge coupled device (CCD) image sensor or acomplementary metal oxide semiconductor (CMOS) image sensor.

The CCD image sensor is an electronic device capable of converting anoptical pattern or image into a charged pattern or an electronic image,comprising a number of photosensitive units capable of modifying,storing and transferring a charge to another photosensitive unit. Indesigning an image sensor, the material is selected subject to thephotosensitivity of silicon. Each photosensitive unit represents apixel. Semiconductor technologies and design rules dominate the arraystructure and matrix structure of the pixels. Signal output from the CCDis modified by means of one or more than one amplifier disposed on theedge of the chip. An electronic image is obtained by a series of pulseswhich sequentially output the charge of one pixel in array after anotherpulse is output to an output amplifier. Then, the output amplifierconverts the charge into a voltage. An external electric circuittransfers an output signal in an appropriate form for detection orpick-up.

The CMOS image sensors operate at a voltage lower than the CCD imagesensor so as to reduce power consumption and facilitate the portability.Each CMOS active pixel sensing unit has an amplifier with bufferingcapability for reading/writing separately. A conventional pixel sensingunit has four transistors and a photosensitive unit. The pixel sensingunit has a transfer gate for separating the photosensitive unit from afloating diffusion having a capacitance, a reset gate interposed betweenthe floating diffusion and a power supply, a source-follower transistorfor temporarily storing the capacitance of a read-out line in thefloating diffusion, and a row of select gates for connecting the pixelsensing unit to the read-out line. All the pixels connected in column-are connected to a shared sense amplifier.

In comparison with the CCD image sensor, the CMOS image sensor not onlyreduces power consumption but also has a generally simple scheme due todecoupling and crystallization characteristics. Hence, a miniature CMOSimage sensor is easy to design, requiring fewer circuits in supportthereof.

FIG. 5 shows a traditional leadless chip carrier package 30 which isgenerally used for a CCD or CMOS image sensor IC chip. The leadless chipcarrier package 30 comprises a transparent cap layer 32 made of glasshaving a supporting layer 35. An anti-reflection coating 34 isinterposed between the glass cap 32 and the supporting layer 35. Amultilayer substrate 36 has a castle-shaped structure 42 with an imagesensor chip 38 provided thereon. An upper lead 40 extends from the chip38 to be electrically connected to a lower lead 44 encased on the bottomand the sides of the substrate 36. The transparent glass cap 32facilitates light transmission to the image sensor chip 38.

The leadless chip carrier package 30 generally has a thickness 46 ofabout 2 mm. When the leadless chip carrier package 30 is used for theimage sensor package 30, a relatively large space is required. In mostcases, an over-sized image sensor restricts the utilization of theleadless chip carrier package 30. In this light, there is a dire need toprovide the image sensors with a new and improved packaging structureand method.

BRIEF SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a packagingstructure of an image sensor module so as to have a compact size,integrally assemble a passive chip processing the signals of an imagesensor into the packaging structure, and simplify the process forfabricating the image sensor module.

Another object of the present invention is to provide a BGA packagingstructure of an image sensor module so as to be capable ofbatch-manufacture and improve the production efficiency of the massproduction.

A further object of the present invention is to provide a packagingmethod of an image sensor module that is suitable for packaging a CCDimage sensor or a CMOS image sensor.

A further object of the present invention is to provide a BGA packagingmethod for an image sensor module so as to significantly reduce thethickness of the package.

To attain the aforesaid objects, a packaging method of an image sensormodule according to the present invention comprises: providing atransparent substrate having a first patterned conductive layer;carrying an image sensor integrated circuit chip having a photosensitiveactive area and at least one passive chip having at least one bond padon the transparent substrate, wherein the photosensitive active areafaces the transparent substrate and the bond pad of the passive chip isdisposed in a direction opposing the transparent substrate; forming aninsulating build-up film over the transparent substrate; and forming aplurality of conductive vias on the insulating build-up film wherein theends of the conductive vias are connected with the bond pad of thepassive chip or the first patterned conductive layer of the transparentsubstrate, while the other ends of the conductive vias are exposed onthe surface of the insulating build-up film.

To attain the aforesaid objects, a packaging structure of an imagesensor module according to the present invention comprises: atransparent substrate having a first patterned conductive layer; animage sensor integrated circuit chip having a photosensitive active areacarried on the transparent substrate and being electrically connected tothe first patterned conductive layer of the transparent substrate,wherein the photosensitive active area faces the transparent substrate;at least one passive chip having at least one bond pad bonded to thetransport substrate with the bond pad opposing the transparentsubstrate; and at least one insulating build-up film over thetransparent substrate, having a plurality of conductive vias and a firstsurface opposing the transparent substrate, wherein the ends of theconductive vias are connected with the bond pad or the first patternedconductive layer, the other ends of the conductive vias are exposed onthe first surface.

The packaging structure of the image sensor package of the presentinvention is efficient in space utilization, as compared with thetraditional image sensor package structure, for example, an LCC package.The thickness of the packaging structure of the image sensor package ofthe present invention is about 1 mm while the thickness of the LCCpackage is about 2 mm. Accordingly, the construction of the image sensordevice with the packaging structure of the present invention isdown-sized compared with the traditional packaging structure of the CCDimage sensor or the CMOS image sensor.

As a rule, an image sensor module includes a number of passive chipscontrolling and processing the signals of the integrated circuit chipsof the image sensor. Therefore, to simplify the processing steps of thefabrication of the image sensor module, the integrated circuit chips ofthe image sensor and the passive chips are buried in a single imagesensor module, and the signals are connected to the outside by thebuild-up method which is commonly applied in the passive chip package.The build-up method is a non-mechanical drilling in association withpressing either a resin coated copper foil (RCC) or a copper foil havingan adhesive tap on the surface of the substrate, wherein the copper foilinterconnects the conductive lines by photo via or laser via.

Additional features and advantages of the present invention will be setforth in part in the description which follows, and in part will beobvious from the description, or may be learned by practice of thepresent invention. The features and advantages of the present inventionwill be realized and attained by means of the elements and combinationsparticularly pointed out in the henceforth appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the present invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of thepresent invention and together with the description, serve to explainthe principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1F are flowcharts illustrating the steps of a packagingmethod of an image sensor module according to the present invention;

FIG. 2A and FIG. 2B are cross-sectional views of a packaging structureof an image sensor module according to the embodiment 1 of the presentinvention;

FIG. 3 is a cross-sectional view of a packaging structure of an imagesensor module according to the embodiment 2 of the present invention;

FIG. 4 is a cross-sectional view of a packaging structure of an imagesensor module according to the embodiment 3 of the present invention;

FIG. 5 is a cross-sectional view of a conventional LCC package used foran image sensor module

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

A thorough process for packaging an image sensor module of the presentinvention is shown in FIG. 1A through FIG. 1F. Referring to FIG. 1A, afirst patterned conductive layer 120 is formed on a transparentsubstrate 110. The method for forming the first patterned conductivelayer 120 is not specifically defined, but is generally by sputtering,evaporation, screen-printing or film-bonding. Next, referring to FIG.1B, an adhesive 150 is coated over the transparent substrate 110 tocarry at least one passive chip 140 having at least one bond pad 145,and an anisotropic conductive adhesive (ACA) 160 or a nonconductiveadhesive (NCA) is coated to carry an image sensor integrated circuitchip 130 having a photosensitive active area 135. As such, thephotosensitive active area 135 faces the transparent substrate 110 whilethe bond pad 145 of the passive chip is disposed in a direction opposingthe transparent substrate 110. The method for carrying the image sensorintegrated circuit chip 130 further comprises a solder bump.Alternatively, the anisotropic conductive adhesive 160 or thenonconductive adhesive can be replaced with another means, for example,a solder ball for soldering. In addition, the transparent substrate 110may further comprise an active chip 141 having at least one bond pad 146carried on the transparent substrate 110, wherein the bond pad 146 ofthe active chip 141 opposes the transparent substrate 110, as shown inFIG. 2B. Besides, the active chip 141 can also be fabricated as abuild-in printing passive device in the subsequent build-up process. Thepassive chip 140 and the image sensor integrated circuit chip 130 arethen bonded to the transparent substrate 110, as shown in FIG. 1C whichis a cross-sectional view taken alone the line I-I′ of FIG. 1B. Then,referring to FIG. 1D, an insulating build-up film 170 is pressed ontothe transparent substrate 110. The method for forming the insulatingbuild-up film 170 over the transparent substrate 110 is not particularlylimited to the pressing and it can be achieved by another method such asspin coating. Furthermore, the thickness of the insulating build-up film170 formed on the transparent substrate 110 is not specifically defined.Preferably, the thickness of the insulating build-up film 170 is lessthan that of the image sensor integrated circuit chip 130 so that asurface of the image sensor integrated circuit chip 130 opposing thephotosensitive active area 135 is exposed in order to increase thecapability of heat dissipation of the image sensor integrated circuitchip 130. In addition, the insulating build-up film 170 is made of amaterial which has excellent electrical isolation and is capable ofbeing processed by laser. In general, a resin coated copper foil (RCC)or a copper foil having an adhesive tap is used to this end. ReferringFIG. 1E, a plurality of conductive vias 180 is formed on the insulatingbuild-up film 170 in which the bottom ends of the conductive vias 180are connected with the bond pad 145 of the passive chip 140 or the firstpatterned conductive layer 120 of the transparent substrate 110 whilethe top ends of the conductive vias 180 are exposed on an upper surface175 of the insulating build-up film 170. The method for forming theconductive vias 180 is not specifically defined, but preferably is bylaser drilling or photolithography. Then, a conductive material isformed in the conductive vias 180 by electroplating so that the signalsof the image sensor integrated circuit chip 130 can be transmitted bymeans of the first patterned conductive layer 120 and the conductivevias 180 while the signals of the passive chip 140 are input or outputby means of the conductive vias 180.

As shown in FIG. 1F, the packaging method of an image sensor modulepreferably further comprises the step of forming a second patternedconductive layer 190 over the upper surface 175 of the insulatingbuild-up film 170. After the second patterned conductive layer 190 isformed, a solder mask layer 220 having a plurality of via-holes 210 isformed over the second patterned conductive layer 190 to protect thesecond patterned conductive layer 190 and prevent moisture from gettinginto the chip. Finally, a plurality of solder balls 230 is formed in thevia-holes 210 of the solder mask layer 220 to complete the image sensormodule package. Even so, the film build-up method can be appliedrepeatedly after the formation of the second patterned conductive layer190. That is, an insulting build-up film, a plurality of conductive viasin the insulating build-up film and a third patterned conductive layerover the insulating build-up film are formed in so order.

Three preferred embodiments of the present invention are describedhereinafter for illustrating the technical merits of the presentinvention.

Embodiment 1: Packaging Structure of an Image Sensor Module

As shown in FIG. 2, this embodiment discloses a packaging structure ofan image sensor module having a CMOS chip. A transparent substrate 110having a first patterned conductive layer 120 formed by sputtering isincluded. A CMOS chip 136 having a photosensitive active area (notshown) is bonded to the transparent substrate 110 with an anisotropicconductive adhesive 160, which is electrically connected to the firstpatterned conducive layer 120 of the transparent substrate 110 and thephotosensitive active area faces the transparent substrate 110.Furthermore, a passive chip 140 having at least one bond pad 145 isbonded to the transparent substrate 110 with an adhesive 150, whereinthe bond pad 145 opposing the transparent substrate 110. An insulatingbuild-up film 170 is coated over the transparent substrate 110 so thatall of the chips carried on the transparent substrate 110 are buried inthe insulating build-up film 170. A plurality of conductive vias 180 isformed in the insulating build-up film 170 by laser drilling. The endsof these conductive vias 180 are connected with the bond pad 145 or thefirst patterned conductive layer 120 while the other ends of theconductive vias 180 are exposed on a first surface 175 of the insulatingbuild-up film 170. The insulating build-up film 170 is thinner than theCMOS chip 136 so that a surface of the CMOS chip 136 opposing thephotosensitive active areas is not covered by the insulating build-upfilm 170. A second patterned conductive layer 190 is formed on the uppersurface 175 of the insulating build-up film 170. A solder mask layer 220having a plurality of via-holes 210 covers the second patternedconductive layer 190 to protect the second patterned conductive layer190. A plurality of solder balls 230 is formed in the via-holes 210 ofthe solder mask layer 220. As a result, a flip chip BGA image sensormodule is completed.

The structure of the image sensor module package in this embodiment ischaracterized by efficient space utilization, as compared with thestructure of the traditional image sensor package. The total thicknesst1 of the image senor module of this embodiment is about 650 μm which isthe sum of the thickness of the transparent substrate 110 and thethickness of the CMOS chip 136. Thus, the construction of the imagesensor device is down-sized compared with the construction of thetraditional image sensor package. In addition, the fabrication of theinterconnecting lines of the passive chip 140 and the interconnectinglines of the CMOS chip 136 is integrated in the same processing step toreduce the processing steps required for the package, theinterconnecting lines herein including the first patterned conductivelayer 120, the conductive vias 180 and the second patterned conductivelayer 190. Moreover, because the back face of the CMOS chip 136 is fullyexposed, the heat dissipation function and operation efficiency areenhanced.

Embodiment 2: Packaging Structure of an Image Sensor Module

As shown in FIG. 3, this embodiment discloses a packaging structure ofan image sensor module having a CCD chip. A transparent substrate 110having a first patterned conductive layer 120 formed by evaporation isincluded. A CCD chip 138 having a photosensitive active area (not shown)is soldered to the transparent substrate 110 with solder balls 230. Thesolder balls are electrically connected to the first patterned conducivelayer 120 of the transparent substrate 110 and the photosensitive activearea faces the transparent substrate 110. An epoxy 240 fills in thespace between the solder balls 230 so that the space area 250 betweenthe photosensitive active area (not shown) and the transparent substrate110 becomes hermetic. Furthermore, a passive chip 140 having at leastone bond pad 145 is bonded to the transparent substrate 110 with anadhesive 150, wherein the bond pad 145 opposes the transparent substrate110. An insulating build-up film 170 is formed over the transparentsubstrate 110 by pressing so that all of the chips carried on thetransparent substrate 110 are buried in the insulating build-up film170. A plurality of conductive vias 180 is formed in the insulatingbuild-up film 170 by laser drilling. The ends of these conductive vias180 are connected with the bond pad 145 or the first patternedconductive layer 120 while the other ends of the conductive vias 180 areexposed on a first surface 175 of the insulating build-up film 170. Theinsulating build-up film 170 is thicker than the CCD chip 138. A secondpatterned conductive layer 190 is formed on the upper surface 175 of theinsulating build-up film 170. A solder mask layer 220 having a pluralityof via-holes 210 covers the second patterned conductive layer 190 toprotect the second patterned conductive layer 190. The plurality ofsolder balls 230 is formed in the via-holes 210 of the solder mask layer220. As a result, an image sensor module is completed.

The structure of the image sensor module package in this embodiment ischaracterized by efficient space utilization, as compared with thestructure of the traditional image sensor package. The total thicknesst1 of the image senor module of this embodiment is about 1 mm, while thethickness of the traditional image sensor package structure is about 2mm. Thus, the present construction is down-sized. In addition, thefabrication of the interconnecting lines of the passive chip 140 and theinterconnecting lines of the CCD chip 138 is integrated in the sameprocessing step to reduce the processing steps required for the package,the interconnecting lines herein including the first patternedconductive layer 120, the conductive vias 180 and the second patternedconductive layer 190.

Embodiment 3: Packaging Structure of an Image Sensor Module

As shown in FIG. 4, this embodiment discloses a packaging structure ofan image sensor module having a CMOS chip. A transparent substrate 110having a first patterned conductive layer 120 formed by screen-printingis included. A CMOS chip 136 having a photosensitive active area (notshown) is soldered to the transparent substrate 110 with solder balls230, wherein the solder balls 230 are electrically connected to thefirst patterned conducive layer 120 of the transparent substrate 110 andthe photosensitive active area faces the transparent substrate 110. Anepoxy 240 fills in the space between the solder balls 230 so that thespace area 250 between the photosensitive active area (not shown) andthe transparent substrate 110 becomes hermetic. Furthermore, a passivechip 140 having at least one bond pad 145 is bonded to the transparentsubstrate 110 with an adhesive 150, wherein the bond pad 145 opposes thetransparent substrate 110. An insulating build-up film 170 is coatedover the transparent substrate 110 so that all of the chips carried onthe transparent substrate 110 are buried in the insulating build-up film170. A plurality of conductive vias 180 is formed in the insulatingbuild-up film 170 by laser drilling. The ends of these conductive vias180 are connected with the bond pad 145 or the first patternedconductive layer 120 while the other ends of the conductive vias 180 areexposed on a first surface 175 of the insulating build-up film 170. Theinsulating build-up film 170 is thinner than the CMOS chip 136 so that asurface of the CMOS chip 136 opposing the photosensitive active areas(not shown) is not covered by the insulating build-up film 170. A secondpatterned conductive layer 190 is formed on the upper surface 175 of theinsulating build-up film 170. A solder mask layer 220 having a pluralityof via-holes 210 covers the second patterned conductive layer 190 toprotect the second patterned conductive layer 190. A plurality of solderballs 230 is formed in the via-holes 210 of the solder mask layer 220.As a result, an image sensor module is completed.

The structure of the image sensor module package in this embodiment ischaracterized by efficient space utilization, as compared with thestructure of the traditional image sensor package. Thus, theconstruction of the image sensor device is down-sized compared with theconstruction of the traditional image sensor package. In addition, thefabrication of the interconnecting lines of the passive chip 140 and theinterconnecting lines of the CMOS chip 136 is integrated in the sameprocessing step to reduce the processing steps required for the package.Moreover, because the back face of the CMOS chip 136 is fully exposed,the heat dissipation function and operation efficiency are enhanced.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the present invention disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the present invention being indicated by thefollowing claims.

1. A packaging structure of an image sensor module, comprising: atransparent substrate having a first patterned conductive layer; animage sensor integrated circuit chip having a photosensitive active areacarried on said transparent substrate and being electrically connectedto said first patterned conductive layer of said transparent substrate,wherein said photosensitive active area faces said transparentsubstrate; at least one passive chip having opposing first and secondsides, said first side bonded to said transparent substrate and saidsecond side opposing said transparent substrate, and said passive chipincluding a bond pad on said second side; at least one insulatingbuild-up film over said transparent substrate, having a plurality ofconductive vias and a first surface opposing said transparent substrate,wherein a first end of at least one of said conductive vias is connectedwith said bond pad and a first end of at least one other of saidconductive vias is connected with said first patterned conductive layer,and wherein second ends of said conductive vias are exposed on saidfirst surface; and a second patterned conductive layer formed on saidfirst surface of said insulating build-up film, wherein said imagesensor integrated circuit chip and said at least one passive chip areboth buried in said insulating build-up film.
 2. The packaging structureof an image sensor module of claim 1, further comprising a solder masklayer having a plurality of via-holes to cover and protect said secondpatterned conductive layer.
 3. The packaging structure of an imagesensor module of claim 2, further comprising a plurality of solder ballsformed in said via-holes of said solder mask layer which is electricallyconnected to said conductive vias.
 4. The packaging structure of animage sensor module of claim 1, wherein the thickness of said insulatingbuild-up film is less than the thickness of said image sensor integratedcircuit chip so that the surface of said image sensor integrated circuitchip opposing said photosensitive active areas is not covered by saidinsulating build-up film.
 5. The packaging structure of an image sensormodule of claim 1, wherein said insulating build-up film is formed bypressing or coating.
 6. The packaging structure of an image sensormodule of claim 1, wherein said conductive vias are formed by laserdrilling.
 7. The packaging structure of an image sensor module of claim1, wherein said image sensor integrated circuit chip is bonded to saidtransparent substrate with an anisotropic conductive adhesive or anonconductive adhesive.
 8. The packaging structure of an image sensormodule of claim 1, wherein said image sensor integrated circuit chip isbonded to said transparent substrate with a solder ball or a solderbump.
 9. The packaging structure of an image sensor module of claim 1,wherein said first patterned conductive layer is formed by sputtering,evaporation, screen-printing or film-bonding.
 10. The packagingstructure of an image sensor module of claim 1, further comprising atleast one active chip bonded to said transparent substrate wherein saidactive chip is interposed between said insulating build-up film and saidtransparent substrate.
 11. The packaging structure of an image sensormodule of claim 1, wherein said passive chip is bonded with an adhesive.